Only because its a worldwide midnight launch, because most EU Countries are in a completely different timezone, its midnight there first.

Correct me if I'm wrong, but it's not a worldwide midnight launch and the servers go live with the Cataclysm patch at midnight PST time, not midnight relative to whatever timezone your server is. I thought all servers were going live at that time, so the count down times should be the same.

Edit: I was right and wrong. It's not a worldwide midnight release but it is going live at different times for EU than for everyone else...